Method of concentrating nitric acid



7 Aug. 29, 1933. H. FRISCHER METHOD OF CONCENTRATING NITRIC ACID Original Filed Nov. 30, 1927 -5beam O hydraried JuZfuric acid exhaust:

ateam ham 8 58am Patented 'AugL'Zi-J, 1933 j a "25 the nitric acid alone. All attempts to obviate invention. In the drawing 30 tion of lower oxides of nitrogen and to great losses Figs. 3 and 4 are a partialsectional view and a H acid), however, contrary to the unsuccessful attogether with the bottom section F having the METHOD OF CONCENTRATING NITRIC non) j Hermann Frischer, Cologne-LindenthaL' e V Germany e H Original application November 30, 1927;1 Serial No. 236,705, and in Germany December6,"19 26,

7 Divided and this application July 30, 1929. .i Serial No. 382,110. I

z oisims; (eras-160)- dilute nitric acid, more especially by means of not more than 1-.3-1.5 tons's ulfuric acid. dehydrating media such as for instance concen-' I prefer operating this process in columns trated sulfuric acid, which are subdivided in sectionscorrespondingj-, This application is a division of application to .theseveraLsteps or; stages-of heating, these Number 236,705 filed under date of November 30; sections being heated singly or in groups of two; 1927. .or three and indirectly with heated liquids or It is an object-of. my invention to provide steam -oi,difierent temperature and pressure, the means whereby such concentration can be carconditions of heating being so. chosen that the ried through at less cost and a' purer product of section containing the fresh dilute acid is heated higher concentration can be obtained than .was oth we the lastsection to the e t h hitherto possible. i i v 0 p Q t In the production of concentrated nitric acid I have furtherfound that itis advantageous to it is of prime importance to extract from the cha the in se i n w h r ter-qua iti dilute nitric acid the greatest possible quantities of acid mixture than was hithertodone, as in so of acid of the highest concentration with the doing I obtain a more uniform concentration of least possible expenditure of the dehydrating the nitric acid and a more perfectdenitration of agent (e. g. sulfuric acid). Hitherto such conthe sulfuric acid. centration has been practiced in columns, into The new process according to this invention has which steam was introduced. in direct contact p d pa y useful fOr h recovery of with the dehydrating medium. The absorption nitric acid from denitration acid. of water fromthe' steam rendered it necessary In the drawing affixed to this specification and to provide for greater quantities of such media iormingpart'thereof is showndiagrammatically than would be required for the concentration of by way'of example an apparatus embodying my- My invention refers to the. concentration-of centratingethe"samequantityofnitric acidwith this drawback by expelling the nitric ,acid from Fig. lis a vertical section of the column built its mixture with sulfuric acid by indirect heating up from annular sections, while proved a failure in view of far-reaching decom- 1 Fig. 2 is a similar View of part of a section pro-' positions taking place, which lead tothe formavided with a different heating system.

of nitric acid. plan view, respectivelmof. a third modification of According to the present invention the dilute heating means. Y V 1 nitric acid is concentrated by indirect heating in Referring first to Fig.1, A, B, C, .D,E, are the the presence of a dehydrating medium (sulfuric superposed annularisectionsforming'the column 90 tempts mentioned above the concentration is form of a kettle. Each section is formed with carried th ll h i Several Step5 distinguished by double walls forming a locating jacket 1. The top he t mp f heating, the f h dilute acid section is surmounted by the cover 3 having inlet solution b in exposed to a p r iv y l w pipes 4 and 5 for the dilute nitric acid and the perature, while in the next following St p it concentrated sulfuric acid, the nitric acid vapours is heated to ahigher temperature, and so on, escaping through the exhaust tube 6, 'Flanged until in the last step the mixture of sulfuric acid sockets 7 are provided on the heating jackets for and the last traces of nitric acid are heated to the introduction of steam, sockets 8 for the exthe highest temperature. In this manner I suchaust of steam or condensate. The heating jack- 1 ceed in obtaining the highest possible yield of ets of sections B andC are connected by bends 9,. nitric acid of highest concentration without sufand so are the jackets of sections D andE. To the fering any losses by decomposition. At the same bottom of section F is fitted a tap socket 10 for time a great part of the dehydrating medium the hydrated sulfuric acidfreedfrOm nitric acid; I

(sulfuric acid) hitherto required is saved. The sections are separated fromeach other-by 1Q While in operating with direct heating by inintermediate plates 11 forming partitions on which ,troducing steam into the column about 2.5 tons are mounted vapour tubes 12 for the passage of of concentrated sulfuric acid containing from nitric acid vapour'e'xpelled from the mixture of 95-97% H2804 were required per ton of dilute nitric acid and sulfuric acid. Overflow tubes 13 nitric acid of about 36 B., I succeed in conlead from the upper to the lower sections, these Q tubes being so arranged that a large body of acid mixture is maintained in each section.

Top section-A may for instance be heated with steam of 102 C. introduced into the jacket. Combined sections B and C may be heated with steam of 2.5 atms; having a temperature of about 120 0., sections D and E with steam of 5 atms. and 145-150 C. Bottom section F may be heated to about 160 C. with steam of 6-8 atms. pressure. The fresh dilute nitric acid solution entering through pipe 4 and mixing with the concentrated sulfuric acid introduced through pipe 5 is freed from the greater part of the nitric acid in the top section which is heated slightly above 100 C. Obviously at this temperature no overheating and no decomposition can occur. When the mixture in this section has reached the top end of the overflow tube 13, some of the mixture will flow down into section B, to be heated there to a higher temperature, whereby part of the nitric acid therein contained is expelled and rising through the vapour tubes 12 in the form of vapour will escape through exhaust tube 6. The same devel-' opment of nitric acid vapours will take place-in the lower sections, the temperaturein which is adapted to the decrease of nitric acid contained in the mixture, until the residual nitric acid is expelled from the dilute sulfuric acid in the bottom section at a comparatively high temperature.

Various means may be provided for heating the several sections. The double-walled jackets may for instance be replaced by cast walls 15 (Fig. 2)

in which are formed or embedded steam coils 16.

parting from the invention I may, however, also arrange a number of radial heating elements in each section, such element, as shown in Figs. 3 and 4, consisting of a flanged tube 18 closed at its inner end, a cover 19 being mounted'on the flanged outer end, said cover being provided with sockets20, 21 for the introduction of a steam pipe 22 andfor the escape of the steam, respectively.

1 7 Various changes may be made in the details disclosed in the foregoing specification without deor sacrificing the ad:

vantages thereof. a

I claim:- H

1. In the concentration of nitric acid, the process which comprises passing a liquid mixture of nitric acid and sulfuric acid through a series of separated zones containing bodies of said liquid mixture heated indirectly, with prevention of local v superheating, to successively higher temperatures,

said temperatures being sufiicient to cause disengagement of nitric acid vapors but insufiicient'to cause decomposition of nitric acid, and passing substantially all the vapors of nitric acid thereby liberated through said zones in a direction counter to the flow of said mixture,'thereby recovering substantially, the entire nitric acid content of said mixture in the form of concentrated nitric acid.

2. The process of claim 1 wherein the first zone into which nitric acid is introduced is maintained at a temperature in the neighborhood of slightly above C. and the last'zone is maintained at a temperature of about 160 C.

HERMANN FRISCHER. 

